Efficiently support full text search of string datatyped columns. Mag Gam raised this issue on the user's mailing list on 24 July 2005; the email thread is titled 'Full Text Indexing'. Mag wants to see something akin to the functionality in tsearch2 (http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/). Dan points out that we may be able to re-use index building technology exposed by the apache Lucene project (http://lucene.apache.org/).
Presumably we want to build inverted indexes on all string datatyped columns: CHAR, VARCHAR, LONG VARCHAR, CLOB,, and their national variants (when they are implemented). We should consider the following additional issues when specifying this feature:
1) Do we also want to support text search on XML columns?
2) Which human languages do we support initially? Each language has its own rules for lexing words and its own list of "noise" words which should not be indexed. Hopefully, we can plug-in some existing packages of lexers and noise filters. We should encourage users to donate additional lexers/fitlers.
3) The CREATE INDEX syntax (for these new inverted indexes) should let us bind a lexing human language to a string-datatyped column.
4) How do we express the search condition? For case-sensitive searches we can get away with boolean expressions built out of standard LIKE clauses. However, in my opinion, case-sensitive searches are an edge case. The more useful situation is a case-insensitive search. Can we get away with introducing a non-standard function here or do we need to push a proposal through the standards commitees? Even more useful and non-standard are fuzzy searches, which tolerate bad spellers.